414 



TITANOTHERES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



a well-elevated ectoloph. In general this series is long, 

 averaging 202 to 208 millimeters in length. The true 

 molars are very strongly dolichocephalic in certain 

 specimens (as in Am. Mus. 1850), in which the antero- 

 posterior considerably exceeds the transverse measure- 

 ment of each tooth. In other specimens, however 

 (as in Am. Mus. 1851, type), the anteroposterior and 

 transverse diameters are more nearly subequal. In 

 most specimens the external cingulum is sharply 

 defined, although there is considerable variation in 

 this respect also. The ectoloph cusps and internal 

 cones are subhypsodont, or elevated (paracone 34 

 mm. high, protocone 23 mm.). The internal cusps 

 (the deuterocones of the premolars and the proto- 

 cones and hypocones of the molars) throughout the 

 series are rounded at the apices and are decidedly 



Figure 350. — Upper incisors and canines of 

 DoKchorhinns hyognathus 



One-half natural size. A, Am. Mus. 1S51, White River, 

 Uinta Basin, Utah, Uinta B 2, side view; B, Am. jMus. 

 1845, White Biver, Utah, Uinta B 2, crown view. 



convex internally as compared with those in the 

 Telmatherium phylum. Vestigial protoconules appear 

 in the molars of Am. Mus. 1850. Small, more or less 

 cingulate hypocones appear variably in m^ A well- 

 defined and sometimes broad internal cingulum extends 

 around the lingual side of the premolars in the more 

 progressive specimens (Am. Mus. 1850, 1851, 1852). 

 P^-p* in crown view appear more subcircular in outline 

 than in Telmatherium. 



Premolars. — Of the superior premolars, p' is sepa- 

 rated by a slight diastema (15 mm.) from the canine 

 and is a bifanged, narrow, laterally compressed tooth 

 (ap. 16 mm., tr. 9) with convex buccal and more concave 

 lingual faces. The posterobasal lobe is becoming well 

 defined. P^ is more subcircular than in M. petersoni, 

 its proportions being 20 by 19 millimeters, a condition 

 which is due to the more anterior position of the deu- 

 terocone. The protocone and tritocone are subequal, 

 , but the protocone is much more prominent externally. 



Figure 351. — Lower incisors and 

 canines of Dolichorhimis hyogna- 

 thus 



One-half natural size. Am. Mus. 1856, White 

 River, Uinta Basin, Utah, Uinta B 2; crown 

 view. 



the tritocone being stdl nearly flat. A rudimentary 

 protoconule is observed (Am. Mus. 1850). In p' 

 (ap. 20 mm., tr. 21) the inner portion of the crown is 

 broader, a rudimentary protoconule is seen, a 

 slight spur foreshadowing the tetartocone extends 

 back from the deuterocone, the protocone exhibits a 

 narrow but sharply convex buccal face, the trito- 

 cone is slightly convex, with a basal cingulum. In p^ 

 the ectoloph rises to 21 millimeters, the external 

 cingulum is more continuous, and the inner side of the 

 crown is relatively broader, the crown measuring 22 

 by 24 millimeters. In 

 these premolars (p', 

 p*) the tetartocone 

 rudiments are of the 

 faintest character; in 

 well-worn teeth they 

 are not perceptible at 

 all. 1>. hyognathus has 

 less progressive tetar- 

 tocones than T. ulti- 

 mum but is very highly 

 specialized in respect 

 to the peculiar sub- 

 circular form of p^-p^. 



D. hyognathus presents a considerable advance 

 beyond D. vallidens and some advance beyond D. 

 intermedius in the elevation of the ectoloph as a whole; 

 the increased symmetry of the protocones and trito- 

 cones, especially in p^, which is a much more progres- 

 sive tooth than in D. vallidens; and the more nearly 

 subcircular form of p^-p^. 



A specific dolichocephalic feature of the inferior pre- 

 molars is the spacing of pi in the midst of the long dia- 

 stema between the canine and p2, as 

 seen especially in the type of D. 

 hyognathus, in which this diastema 

 measures 52 millimeters, the diastema 

 in front of pi measuring 25 and 

 that behind 14. These diastemata 

 naturally increase as the individuals 

 advance in age, and they are affected 

 by individual growth, by the stage of 

 evolution, and by the sex. In the fe- 

 male (Am. Mus. 1856) the total dia- 

 stema between the canine and p2 is 

 42 millimeters, nearly in the center 

 of which lies pi. The lower pre- 

 molars are well preserved in Am. Mus. 1856, from 

 which the following descriptions and measurements 

 are taken: Pi is a laterally compressed tooth, measur- 

 ing (ap. by tr.) 15 by 8 millimeters, with the 

 posterobasal lobe well defined and bearing a dis- 

 tinct cusp. In p2 (ap. 23 mm., tr. 11) the protocone, 

 which is somewhat less prominent (16 mm.), rela- 

 tively, exhibits the antero-internal concavity and a 

 rudiment of the antero-internal cusp ( = paraconid); 

 the posterior lobe (=talomd) is more distinctly of the 



Figure 352.-Left 

 upper canine of 

 Dolichorhinus 

 hyognathus 



One-half natural size. 

 Am. Mus. 1850; ex- 

 ternal view. 



